Small mammals and reptiles can be very diverse and abundant in modern ecosystems, but small dinosaurs (less than 100 kg) are considerably less common than large ones in the fossil record. (sciencedaily.com)
Indeed, modern ecosystems depend on the persistence of bacteria and fungi and other relatively very simple and archaic life forms to break down dead organisms and recycle nutrients. (religion.blogs.cnn.com)
«This is despite the fact that 48 million years of species turnover and evolution separate the Messel lake ecosystem from modern ecosystems.» (sciencedaily.com)